1. Technical Field
The present invention relates to a vibration actuator. In particular, the present invention relates to a vibration actuator that rotates a rotating axle via vibrational movement, and to an image capturing apparatus including this vibration actuator.
2. Related Art
A known vibration actuator converts ultrasonic vibration into rotational movement or linear movement. This vibration actuator includes electromechanical transducers that are formed using piezoelectric material. The vibration actuator converts vibration, which is generated by applying a periodically changing drive voltage to the electromechanical transducers, into rotational motion or linear motion, and transmits this motion to an external drive receiving portion.
As an example of such a vibration actuator, U.S. Pat. No. 6,940,209 discloses an ultrasonic lead screw motor. This ultrasonic motor includes (i) a rectangular elastic body having a through-hole with a screw groove formed near the ends thereof on the inner surface, (ii) four electromechanical transducers mounted respectively on the four sides of the rectangular elastic body, and (iii) a screw shaft that is inserted and screwed into the through hole. Vibration of the elastic body caused by applying a periodic drive voltage with a phase that is sequentially delayed by π/2 to the four electromechanical transducers is converted into screwing movement of the screw shaft, and so the screw shaft moves in the axial direction.
In the ultrasonic motor of Patent Document 1, however, the rotational force is achieved via linear contact between the threaded portion of the screw shaft and the screw groove of the through-hole, and so in order to achieve a large amount of torque, the clearance between the threaded portion of the screw shaft and the screw groove of the through-hole must be decreased or a biasing member must be used. Even when the clearance between the screw groove and the threaded portion of the screw shaft is decreased or a biasing member is used, rotation occurs with the threaded portion being pressed against the screw groove, which causes extreme wear on the threaded portion and screw groove.